1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device having, for example, a field-effect transistor.
2. Description of the Related Art
When a nonvolatile memory such as a flash memory and the like is manufactured, there is a problem that variation of threshold voltage (Vth) tends to occur after wafer processing thereof is completed. A main cause of such occurrence is estimated that unnecessary electric charges are injected into a floating gate in wafer processing.
Conventionally, in order to cope with this problem, there is proposed an art in which a control gate is connected via plural wirings to a so-called protective diode at manufacturing a flash memory, as disclosed in Patent Document 1 and Patent Document 2.
[Patent Document 1] Japanese Patent Application Laid-open No. 2002-43446
[Patent Document 2] Japanese Patent Application Laid-open No. Hei 7-183502
However, even with these conventional manufacturing methods, it is impossible to sufficiently restrain the threshold voltage variation resulting from the injection of the electric charges into the floating gate at manufacturing.